Litter stretcher-bar assembly



Nov.30,194s. v THOMSON 2,455,027

' LITTER STRETCHER-BAR ASSEMBLY Original Filed Aug. 24, 1942 4 Sheets-Sheet 1 airzaeif 771022302 Li :9, I

Nov. 30, 1948. I 3 THOMSON 2,455,027

LI TTER STRETCHER-BAR AS SEMBLY Original Filed Aug; 24, 1942 4 Sheets-Sheet 2 LITTER STRETCHER-BAR ASSEMBLY Original Filed Aug. 24, 1942 4 Sheets-Sheet s .Nov. 30, 1948. s. G. THOMSON I LITTER STRETCHERBAR ASSEMBLY 4 Shets-Sheet 4 Original Filed Aug. 24, 1942 Patented Nov. 30, 1948 Ni'iE, S

s. T E S Substituted for application Serial No. 455,906, August 24, 1942. This application October 9. 1946, Serial No. 702,294

3 Claims.

This application is substitute for Serial No. 455,906 which became abandoned on September 21, 1946.

This invention relates to litters such as are used to transport persons who may be incapacitated by illness or injury,

More particularly the invention relates to litters which may be folded for storage or transportation.

In the usual type of folding litter the structure includes a pair of side poles, jointed or rigid, a litter bottom of flexible material such as canvas or the like extending between the poles, and jointed means connecting the poles. The jointed means is so arranged that the poles may be held widely spaced to tension the litter bottom or may be brought close together so that the structure takes up only a small amount of storage space.

As usually constructed the jointed means, preferably termed the stretcher bar assembly, comprises a pair of rigid members or struts having ends connected by a pivot bolt and having their remaining ends pivoted to the poles, at least two of these assemblies being used for each litter. The pivotal connection between the struts is normally located midway between the poles.

Pivotal connections directly between the struts of each assembly are lacking in the necessary rigidity, when the litter is expanded for use, to enable the litter to withstand the rough usage and wear to which such litters are usually exposed. Moreover the stretcher-bar assemblies of litters usually bow downward at the joint so that when a person rests on the litter the bottom will not engage on the stretcher-bars and cause discomfort to such person. Thus, in service the ends of the struts at the poles are above the midjoint a certain distance and this distance constitutes a moment arm for the forces due to the weight on the litter bottom. A very heavy stress, acting in a vertical plane, is thus set up in the mid-joint with consequent tendency to bend the pivot.

It is one important object of the present invention to provide a novel link connection between the proximal ends of such stretcher-bars whereby no pivots are used at exact mid-length where downward buckling force is maximum, and whereby reinforced link walls of large area and sectional strength are held to a close sliding fit and rigid engagement with a considerable length and substantial area of the ends of the strut members.

In collapsing folding litters of the kind above mentioned it is very important that the folded alinement with the litter poles. When a litter is collapsed the poles should not only lie close together but one must not project lengthways beyond the other: In the ordinary construction wherein the struts are directly pivoted together on a single pivot the mid-joint can swing laterally and this lateral swinging causes projection of one pole lineally beyond the other.

A second important object of the invention is to provide a novel form of mid-joint for stretcher-bar assemblies whereby the mid-joint, upon collapse of the litter, will be constrained to lie centrally of the space between the litter sides or poles and the poles will be constrained from movement longitudinally with respect to each other when the litter is fully collapsed.

In litters of this character, especially in those for war use in transporting the wounded, it is highly desirable that the structure be as light as is consistent with proper strength and rigidity.

A third important object of the invention is to provide a novel stretcher-bar assembly wherein the construction is such as to permit the use of very thin walled tubes so arranged and formed as to produce a structure of great strength and rigidity.

A fourth important object of the invention is to provide a novel method of bending thin walled tubes for this purpose whereby the tube will be bent without over stretching the material on the convex side of the bend or decreasing the wall thickness at any place or point so as to cause complete collapse due to buckling of thin walls.

With the above and other objects in view as will be presently apparent, the invention consists in general in a novel method of bending thin walled tubes and in certain novel details of construction and combination of parts hereinafter fully described, illustrated in the accompanying drawings and particularly claimed.

In the accompanying drawings like characters of reference indicate like parts in the several views, and Y Figure 1 is a view, partly in elevation and partly in section, showing one form of stretcher assembly as constructed 'in accordance with this invention.

Figure 2 is a plan view partly in section and showing parts disclosed in Figure 1.

Figure 3 is a section on the line 3-3 of Figure Figure 4 is a section on the line 4 4 of Figure Figure 5 is a fragmentary section showing a modification of the middle joint of the assembly as shown at the left of Figure 2.

Figure 6 is an enlarged detail section on the line 6-6 of Figure 1.

Figure 7 is a view similar to Figure 6 but showing a modified form of tube cross-section.

FigureB is a similar view but showing a second modification of the tube cross-section.

Figure 9 is a cross-section showing one form of fiat end on a circular thin walled tube as used in this invention.

Figure 10 is a view similar to Figure 9 but showing a modified form of tube end, 7

Figure 11 is a bottom plan view of a portion of a litter showing diagrammatically the relation of the stretcher-bar assembly to the remainder of the litter.

Figure 12 is a, side elevation of the parts shown in Figure 11.

Figure 13 is a fragmentary bottom plan view or a modification or the tretcher-bar assembly, the view showing the poles and legs of a litter with the poles in the position assumed when the litter is folded.

Figure 14 is a plan View, partly in section showing the struts and connecting member with the litter expanded.

Figure 15 is a cross-section through the con necting member ofthi's form of assembly showihg ohe form of pivot for connecting a strut and said member.

Figure 16 is a ersp'ectiveview showing a bushing and washeras used in the form shown in Fi are 15, the parts being disassembled. 4

1 Figure 17 is a plan view of a portion of a strut and modified connecting member.

Figure 18 is a section on the line iii-'48 of Figlli 1'7. 4

Figu e 19 is a view similar to Figure 17 but showing a second modification of th'blit'er Dice for this form of assembly Figure 20 is a, section an the line ire- 2o of Figure 19.

Figure 21 is a view similar to Figure 18 but showing it Stillfurthl IIlOdifiCatlbh Of'tll Cellt'er piece.

Figure 22 is a reduced detail side elevation of one of the struts used herein.

Figure 23 is a longitudinal vertical section showing a slight modification of the constructi'on in Figure 1. g g Figure 24 is a section oh the line 24- 24 of new .r t c .y

Figure25 it; view siii 'iiar to Figure 5 but showing a slight modification thereof. Fi ure 25 is an elevation of a hint of assembly wherein the cohnecting member is of sii s e u a i imr a. i Figure 2'7 a plan iew partly in section of the form shown in FigureZB;

. new??? is avieWs m ler t6 re ew but showing the assembly applied to a portion of a litter and the latter folded. I

Figure 29 is an enlarged fragmentary section bathe line 2}l29 of Figure 26. i H 30 is a View similar to Figure 2? but showing a packing strip or spacer used therewith.

Figure 31 is a section Figure 30.

Figure 32 is a View of the blank from which the tubularconnector of Figure 27 is made.

33 is a View 6f th blahk from. which thepacking strip 01 Figure 30 is made.

F'i gl'ir 34: iS a; diagfairimatidVi-W Silo Wing ceron the line 31-31 of sior'i them the es PS Pivot tain steps in the manufacture of one form of a joint member forming part of this invention.

Considering first the general relation of the present invention to the remainder of a litter to which it may be applied, there has been shown inFigures 11 and 12 a portion of a litter including a pair of handle provided poles A between which extends a webbing B of fabric or other suitable material. Legs C extend downwardly from the poles A and are arranged in pairs with the legs of each pair opposite each other when the litter is extended as in Figure 11. The poles are held apart, with the litter in use, by stretcherbar assemblies each of which, in the present invention, includes a pair of struts D having their outer ends pivoted to the legs C and their inner or proximal enas spaced by and pivoted to a center member or elongated hinge E. It is to be noted that this arrangement of a. pair of struts and elongated hinge forms a very important ieature oi this invention for reasons presently to be explained and the same general arrangement is carried out through all forms of this invehtion. since the literal characters Ato E are made merely to indicate the general parts of the structure the same characters will be used throughout to indicate, in general, corresponding parts in the various forms shown, the specific constructions of such forms being indicated by reference numerals. V

In the forms of the invention shown in Figures 1 to 10 the leg C is shown as consisting of a lower portion Ill and an upper portion II. The pole A rests in a saddle l2 which is held in spaced relation to the portion 1! by a spacer sleeve l3.

A bolt l4 passes through these parts and holds them together. The speoific construction of these parts is unimportant to the present invention except that the spacing of the parts It and i2 permits proper swinging movement of the strut D and the bolt and sleeve form a pivotal connection between the outer end of thstrut and the litter pole A. i

The "struts, as here shown, are thin walled square tubes 15 reversely curved to ariih downwardly as snowh in Figure 1. The outer ends or these tubes are pivoted, as above set forth, on the sleeves 3. The member E in the form ShQiVii in Figures 1 to 4 consists of a'l'aterally open channel member having parallel flanges it connected by aw'eb H. The proximal ends of the struts D engage between the hinges i6. one orb'oth ends or each tube l5 fitted a reinforcing sleeve [8 preferably of coiisiirlerably thicli'er wall'dim'enpins hr rivets 19 pass through the flanges theifiree edges these pins o pass 1; ugh the pro iitjtfs ends iii the struts p. A sleeve illjmay s irround each pin between the upper and lower sides of the l 5 and'the se si'desare held from contact with the flanges l6 bywa's'hers 2i. Stop pins 22 eiitehd between the fiaiiges i6 and are so positioned as to be engaged by the struts D, as shown in Figure 25wh'ei1 thestruts have swun in opening movement of the litter, slightly beyond thepoirit at which th'eaxe s or the struts 11 in a 'c'o'inindn plane. This position or the member E may be convehientlytei'med as beyond thedea'd center and'thisiterm will be used in what follows.

It will be noted that the tubes is are thin walleiitubes To beta s uch tub'es without to distorting them that they are weakened at the bends has long been deemed impra-ctical und'e'r ordiiiary shoii oiiditions'because the convex side of thtiiii'e at'siih a'bendis'strtcha longitudinally and thus reduced in wall thickness unless the convex tube wall is allowed to flatten at this point. I have found that pressing the tube Wall so that a longitudinal groove or inset 23 is formed therein has the eflect of causing the tube to bend without stretching the opposite side which, by this operation, becomes the convex side of the bend. Moreover, the extent of displacement of the insert portion 23 is not sufiicient to stretch the tube wall at this point. To accomplish this the tube does not need to be originally square but, as shown in Figure '7 a circular tube 2 3 may be provided with a similar inset 25. I have also found that, for certain purposes such insets may be used to increase the stiflness or resistance to bending and in Figure 8 a tube 26 is shown as provided with insets 2! on opposite sides. Such a tube will have resistance to bending out of a plane passing through the side walls centrally between the insets.

If it is preferred the struts may be made of circular tubing such as is shown at 28 in Figures 9 and 10, and the ends may either be flattened as at 29 or pressed to square cross-section as at 30.

In Figure 5 a modification of the member E is shown. In this form the flanges 3i (one only is shown) are connected by a web 32 having ends 33 offset towards the free edges of the flanges and these ends constitute stops replacing the pins 22 when the member E has moved beyond dead center. The pivot pins l9 are used in this form for connecting the struts.

In the forms of the invention shown in Figures 13 to 21 the struts D are formed of flat bar metal as shown at 35. In Figures 13 to 16 the construcin parallel planes. The purpose of this is to produce a downwardly arching effect. One end of each strut is pivoted on a bolt 34 to a pole A. The connecting member is similar to that shown in Figure 3, having a web 35 and parallel flanges 35. However the flanges 36 are relatively narrower than those shown in Figure 3 for purposes presently explained. The flanges 36 are provided at each side of the center with o posed openings 36' wherein is fitted a bushing 31 having on one end a flange-like head 38. Each strut 33' is provided with an opening 39 wherethrough the bushing passes. A bolt 4!! passes through the bushing and between the head of this bolt and on the end of the bushing is a washer it. By this means a very secure pivoting of the struts 33' to the connecting member is attained and the flanges 36 cannot be drawn toward each other to pinch on the struts and interfere with their pivotal action. The position of the pivots is such that, when the member E has moved beyond dead center the struts, as shown in Figure 14, will engage the end edges of the web 35, these edges thus forming stops.

In the form shown in Figures 17 and 18 the connecting member is formed by a plate 42 of elongated rectangular shape. At each end of one long side of the plate is an upstanding stop member 43 secured in position by a rivet M. At each side of the center the plate 42 is provided with an opening 85 wherethrough passes a bolt Mi having a head #32 between which and the plate 42 is a bushing 48 which thus properly spaces the head from the plate. On the bolt is a washer 49 which rests against the under side of the plate 42 and a nut 50 serves to secure the bolt. The struts 33' have each a hole 55 which receives the bushing 48 and the stops 13 each have a head 52 which overlies the respective strut 33' when the litter is ready for use.

In the form shown in Figures 19 and 20 two rectangular plates 53 are secured in spaced relation by rivets 56 adjacent the corners of one longitudinal side. The middle parts of the opposite longitudinal edges are secured by a yoke 55 and rivet 56. Pivot pins 5i extend through the plates and through the struts 33. In this form the rivets E l form the stops for limiting the pivotal movements of the struts when the part E has moved beyond dead center, and the yoke 55 forms stops to prevent swinging in closed position.

The connecting member E of Figure 21 is similar to that shown in Figure 15 but the web 58 has one wide flange 59 and one narrow flange 60, the strut 33 being pivoted to the wide flange by the same pivot arrangement as in Figure 18. Similar to Figure 14, the ends of the web 58 constitute stops for the struts.

The form shown in Figures 23 and 24 is a slight modification of that shown in Figure 1. In this form the holes in the struts it for the pivots iii are spaced considerably further from the proximal ends of these struts so that the struts have short arms 6!. Connecting the flanges it are stop pins 62 which are engaged by the arms 6! when the litter is folded. This arrangement hinders one pole A from shifting longitudinally of the other pole as the connecting member E must change its angular relation to the struts D before the poles can thus shift and the engagement of the arms El and stops prevents this angular change.

In Figure 25, which is a slight modification of Figure 5, the provision of the short arms 6| on the strut enables the inclined portions 63 of the web 32 to act as stops as in the last mentioned form.

In any of the tubular constructions the ends may be closed by plugs 64.

In the form of the invention shown in Figures 26 to 33 the connecting members E is made from a blank of sheet material having a rectangular central or body portion bent along fold lines 65 to provide a web or rear side 66 and a pair of flanges or top and bottom sides 61. The blank is provided at the edges opposite the web part with lips 68 which, when the blank is folded with the lips bent toward each other on the fold lines 69 contact at their free edges and form the front side of the member E. These lips are so proportioned that, when the edges contact, the flange portion 61 will be parallel, and the free edges of the lips afford stops for struts when in closed position. These stop-edges are notched to aliord clearance for the tabs of the spacer shim as shown in Figure 26. This clearance permits the use of shims of different thickness without affecting the stopped position of the struts. The contacting edges of lips 68 may be welded or cemented so as to aflord the stiffness of a solid rectangular tube in resisting the vertical bending force. Moreover the blank has tabs 10 at the ends of the part 66, these tabs being bent forwardly to form stops as best seen in Figures 2'7 and 30. The free corners of the flanges 6'! are connected by pins or rivets H on which are pivoted the usual struts 12 having short arms 13 of such length that the ends of these arms engage the steps 70 when the litter is folded. These tabs may be omitted if desired, the lips being depended upon for stops.

Referring especially to Figures-27, 30 and 33 it will be noted that when the member E has moved beyond dead center the remote ends of the struts will lie slightly closer than when the struts D are in alinement. Consequently there will be some relaxation on the litter bottom B. Due to imperfect adjustment or wear of the parts the member E may move too far beyond dead center and the looseness of the bottom B be excessive. In order to prevent or overcome this undesirable condition, the piece shown in Figure 30 may be used. This consists of a spacer or shim 14 which may be fitted against the inner faces of the lips and there held by tabs 15 bent around these lips as shown in Figure 30.

It will be seen that the lips in Figure 2'? and this shim 14 in Figure 30 constitute stop means for the strut ends 13 to prevent the member E from having too great movement past the dead center.

As shown in Figure 31 a spacing sleeve T6 may be employed in this form as well as in other forms of the device.

It will be seen that Figure 29 shows an illustration of the simplest form ot'construction, in which the struts D may be made of any suitable material, tubular or solid, without spacer sleeves and relying on the abutting end lips 68 to hold the engaging faces between struts D and walls 61' to a close sliding fit against the tension of the pivot pin or bolt.

Figure 34 illustrates a modification of the blank shown in Figure 32 with the tabs omitted. Here the blank 16 maybe cut from a'strip I! of metal or appropriate width by punching transversely of the strip as "at18 thus forming the notched lips I9. Preferably, the punching machine is arranged to bend the lips as shown at 8B. This forms'a method of cutting theblanks which is very economical when it is desired to use narrow strip metal for the purpose since little waste or scrap is made. However, I may cut the blanks from wider sheets with the tabs 10 in use. This I accomplish by staggering rows of blanks so that the tabs ill of one row are formed from the material of the next row.

It is to be "understood that the members D must fit closely against the member E so that the latter reinforces the former and the former reinforces the latter and thus stiffness is added to the center of the stretcher-bar assembly to resist bending due to the remote ends of members D being higher than their proximal ends.

Having thus described the invention, what is claimed is:

l. A mid-joint for litter stretcher-bar assemblies including a pair of proximal and spaced stretcher-bar ends, a channel like member in eluding a web and a pair of flanges, said ends fitting closely between said flanges, pivot pins passing through said flanges and ends, and lips on the free edges of the flanges against which the said ends tend to engage upon expansion of the litter.

2. A mid-joint for litter stretcher-bar assemblies including a pair of proximal and spaced stretcher-bar ends, a channel like member including a web and a pair of flanges, said ends fitting closely between said flanges, pivot pins passing through said flanges and ends, lips on the free edges of the flanges against which the said ends tend to engage upon expansion of the litter, and a shim interposed between said lips and said ends.

3. In a litter, including a pair of side poles, a spreader-bar connecting said poles and comprising a mid-length link having oppositely disposed sides, a pair of struts of tubular cross-section connected at spaced points by pivot pins extending between said sides, said strut ends each having a close sliding fit with said sides for the full length of said end lying within the length of said link and re-iniorcing tubes fitted within each said link engaged strut end.

SAMUEL G. THOMSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain Aug. 17, 1922 Italy May 4, 1936 Number Number 

